but you know what? I'd give it to them, or let them trade in a class feature level or somesuch for the ability.
Think about it, just how frequently is it that this barbarian will fell a foe, on a charge, in a single hit. It can happen, sure, but it's relatively unlikely.
However, let's say this Barb tries to do a "dance of death" all the time. He still has to activate his spring attack (this is key), run up, fell the foe in a single hit, and then move on to the next, and have enough moves to make it if they're significantly spaced apart.
Actually, here's what you do with that Player, allow him to choose an Animal (or a few) that his tribe reveres. Then remove uncanny dodge, trap sense, and improved uncanny dodge.
In return they get the dodge feat, the mobility feat, and "berserkergang".
Berserkergang: This feat duplicates the feat "Spring Attack" with one significant difference. While raging, a character with the cleave feat may use their remaining movement squares after successfully cleaving a foe, in order to strike an additional foe.
